The present invention relates to certain overbased metal salts useful as additives for lubricants based on oils of lubricating viscosity. More particularly, it relates to metal carboxylates of alkylene bis-phenol alkanoic acids and related hydroxy carboxylates. These materials, as well as corresponding neutral salts and certain lactones, are particularly useful as additives for marine diesel lubricants.
The field of lubricant technology is characterized by a never-ending search for improved lubricants and additives. Additives, essential for satisfactory performance of lubricants for all manner of modern engines, serve many roles, including those of providing detergency, antioxidant properties, and suspension of contaminants. The latter function is particularly critical in engines which burn fuel containing asphaltene components, since asphaltenes are often found to contaminate the lubricating oil through blow-by past piston rings. The additives of the present invention, besides their general utility as detergents and antioxidants in many applications such as general diesel applications, are particularly useful in marine diesel engines. Marine diesel engines are typically two- or four-stroke compression ignited engines commonly used in ships for main propulsion or auxiliary power generation applications, or in stationary land-based power generation applications. Marine diesel engines are commonly designed to run on a variety of diesel fuels from good quality light distillate fuel with low sulfur and asphaltene content to poorer quality intermediate or heavy fuels like "Bunker C" or residual fuel oil with generally higher sulfur and asphaltene content. Four stroke engines designs have crankcase oil systems which can become contaminated with diesel fuel either through blow-by or fuel leakage directly into the lubricating oil. Hence the present lubricants are particularly useful in providing asphaltene suspension in lubricants which are employed in the lubrication of such engines.
PCT Publication WO 93/21143, Blystone et al., published Oct. 28, 1993 discloses metal carboxylates of alkylene bis-phenol alkanoic acids useful as additives for fuels and lubricants.
U.S. Pat. No. 5,281,346, Adams et al., Jan. 25, 1994, discloses lubricants for two-cycle engines comprising a major amount of at least one oil of lubricating viscosity and a minor amount of certain compounds of the general formula A.sup.Y- M.sup.y+. A is an anion containing group with a carboxylic aromatic structure.
U.S. Pat. No. 2,933,520 to Bader relates to compounds represented by the formula ##STR1##
in which R.sub.1 may be hydrocarbon, halogen, R.sub.2 is hydrocarbon, e.g., alkylene other than methylene and containing at least two carbon atoms and containing up to 10, 12 or even more carbon atoms, Ar groups are aromatic rings, unsubstituted or substituted with alkyl, halogen, nitro, sulfo and others, the nature of each of these groups affecting properties such as boiling point, solubility, toxicity, and bactericidal, fungicidal, insecticidal and like properties.
U.S. Pat. No. 3,038,935 to Gerber et al. teaches the preparation of compounds of the formula ##STR2##
wherein each R is an aliphatic, cycloaliphatic or aromatic radical, Me is Na, K or Li, by reacting alkali metal salts of hindered phenols with dichloroacetic acid. Products are said to be useful for production of rubber auxiliaries, mineral oil additives and stabilizers for plastics.
U.S. Pat. No. 3,133,944 to Christensen teaches heavy metal salts represented by ##STR3##
wherein the R.sub.1 is alkyl of 1-4 carbons, R.sub.2 is alkylene of 2-6 carbons and Ar is an aromatic group which may be substituted with one or more methyl groups and others. The salts are said to be adapted to retard or prevent the growth of biological organisms, particularly molds and mildews.
U.S. Pat. No. 3,471,537 to Berke et al. teaches diphenolic compounds of the formulas ##STR4##
wherein X and X.sup.1 are halogen or hydrogen, salts and derivatives as useful for germicides and antiseptics and disinfectants.
U.S. Pat. No. 4,828,733 to Farng et al. relates to copper salts of hindered phenol carboxylic acids.
U.S. Pat. No. 4,627,928, Karn, Dec. 9, 1986, discloses basic magnesium salts of substituted aromatic hydroxy carboxylic acids (e.g. salicylic acids) which can be used in lubricating oils.
A wide variety of metal-containing compounds have been employed, with varying degrees of success as lubricating oil additives. Illustrative are detergents of the ash-containing type. These are well-known in the art and include Newtonian and non-Newtonian neutral and overbased salts of alkali, alkaline earth and transition metals with, for example, sulfonic acids, carboxylic acids, salicylic acids, phosphorus-containing acids, phenols and the like. Among the many publications which disclose overbased metal salts and their method of preparation and use is U.S. Pat. No. 3,429,231, McMillen, Jan. 27, 1970 and U.S. Pat. No. 4,627,928, Karn, Dec. 9, 1986.